More than 25,000 of nearly 46,000 miles of transmission pipe were laid prior to 1970, some dating to the Great Depression, according to the Houston Chronicle investigation.

Federal regulators warned companies more than 20 years ago to reconsider the use of all pipelines built with lower-quality welding techniques that were widely employed in pipe factories prior to 1970, documents show. Also a potential problem is some aged protective coating on pipes that actually can make them more vulnerable to corrosion, the newspaper reported.

“Older pipelines have properties that are inherently inferior,” said John Kiefner, a pipeline integrity consultant.

The Texas Railroad Commission has imposed stiffer inspection requirements on pipeline companies than the federal government. The state agency is considering tighter regulations.

The newspaper, which examined federal and state records, reports there is a shortage of government inspectors to get the job done.

About 21,000 miles of interstate natural gas transmission pipelines are under federal jurisdiction, not the Texas Railroad Commission.

Congress began imposing federal construction standards on new natural gas pipelines in 1968, resulting in major improvements in welds, coatings and pipeline inspection techniques.

Charles Yarbrough, vice president of rates and regulatory affairs at Atmos Pipeline-Texas, one of the state’s largest pipeline operators, said pipe pulled from the ground in West Texas, where conditions are generally dry and corrosion is not as big an issue, can appear fairly new after three-quarters of a century.

“New pipe going in the ground is around $1 million to $1.5 million a mile,” said Yarbrough. “It is not something where you want to just say, ‘It is getting old, let’s go and replace it all.’?”